After upgrading some solutions to the new Visual Studio 2010 RTM and expecting automatic migration would do the trick, I bumped into a problem. The problem is that Unit Test project will be automatically upgraded to use .NET Framework 4.0 even if you explicitly choose not to do so in the migration wizard!

But there’s more…if you try to downgrade your project to use .NET Framework 3.5 with Microsoft Test projects (MSTest), well you just can’t.

Framework Version

A little strange, but I guess the reason is that new environment does not support old test runtime and there you have it: another good reason to use an open-source and mature framework when possible.